Hybrid drives may incorporate hard disc drive (HDD) and solid-state drive (SSD) technology. The SSD of the hybrid drive may use NAND memory as a cache for the HDD. The capacity of the NAND is small compared to the overall drive capacity and thus is typically used as a persistent (e.g., survives a power failure) cache to the HDD. The NAND is managed like a SSD device and utilizes a flash translation layer (FTL) to map logical data units to physical locations in the NAND memory. The FTL is generally sized to map the NAND capacity. As the NAND space and HDD space are separate, a cache layer may utilize a separate mapping scheme to map SSD logical data units to space to HDD logical data units.